Life Cycle of Stars

Star Formation and Stellar Nursery

Nebulae are the birthplaces of stars, composed of gas, dust, and other materials.
Gravitational forces pull these materials together into clumps, leading to an increase in density and temperature at the core.
As temperature increases, the core starts glowing, creating a protostar.

Transformation into a Main Sequence Star happens when core temperature reaches a point where nuclear fusion starts.
Nuclear fusion in stars involves the combination of hydrogen atoms to produce helium, releasing a massive amount of energy as radiation.
Most stars, including our Sun, are in this stage for the majority of their existence, roughly 90%.

When the hydrogen fuel in the star’s core runs out, fusion stops, causing the core to contract under gravity.
This contraction increases the core temperature, causing the outer layers of the star to expand, and they turn red due to cooling. This stage is the Red Giant phase for smaller stars and Red Supergiant for larger ones.

For smaller stars like our Sun, after the Red Giant phase, the outer layers are blown off to form a Planetary Nebula, and the hot core that remains is a White Dwarf.
Over billions of years, the White Dwarf cools and dims until it becomes a Black Dwarf.

For more massive stars which become Red Supergiants, nuclear fusion reactions continue past the helium stage, creating heavier elements.
When the process reaches iron, energy can no longer be harvested from fusion, leading to a sudden implosion of the core followed by a rapid explosion known as a Supernova.
If the star was big enough, the core remnant will be so dense that it forms a Black Hole. If the star was slightly less massive, it may form a Neutron Star.

The life cycle of stars is critical to the universe because it facilitates the production and distribution of heavy elements. These elements are necessary for the formation of other objects, such as planets and life as we know it.